The invention relates to software piracy prevention. More specifically, the invention pertains to a novel method of protecting digital data against unauthorized copying and use.
Digital media have become popular carriers for various types of data information. Computer software and audio information, for instance, are widely available on optical compact disks (CDs). Recently, the digital audio tape (DAT) has gained in distribution share. The CD and the DAT utilize a common standard for the digital recording of data, software, images, and audio. Additional media, such as multimedia compact disks (MCD), digital video disks (DVD), super density disks, and the like, are making considerable gains in the software and data distribution market.
The substantially superior quality of the digital format as compared to the analog format renders the former substantially more prone to unauthorized copying and pirating. Copying of a digital data streamxe2x80x94whether compressed, uncompressed, encrypted or non-encryptedxe2x80x94typically does not lead to any appreciable loss of quality in the data. Digital copying thus is essentially unlimited in terms of multi-generation copying. Analog data with its substantial signal to noise ratio, on the other hand, is naturally limited in terms of multi-generation and mass copying.
The advent of the recent popularity in the digital format has also brought about a slew of copy protection systems and methods. These are generally grouped in categories such as encryption, copy protection, and content extensions.
Prior art methods of preventing unauthorized copying of copyrighted and protection-worthy data do not attain a particularly high degree of protection.
Encryption, which is used in the digital and the analog format, essentially scrambles the information. The data stream can be made usable only with the proper key. It has been found that encryption is usually easy to crack. Once the key has been found by a copy pirate, the information may be freely multiplied without encryption.
Software copy protection was widely used during the early days of the personal computer. However, software manufacturers essentially stopped copy protection once it was found that, on the one hand, virtually all copy protection codes would be quickly broken by hackers and, on the other hand, the development of new types of copy protection was becoming prohibitively expensive. Furthermore, non-protected programs soon turned out to become so widely usedxe2x80x94even though many copies were unauthorizedxe2x80x94that the additional sales could largely make up for the bootleg losses.
Several popular programs use a system in which an installation key is delivered with the original program packaging of the data carrier (e.g. CD or floppy). The installation key is required before the program data can be installed on a PC. It is thereby easily possible to copy the key together with the data content of the CD any number of times and to thus distribute and bring into circulation any number of pirated copies.
Another established protection mechanism comprises preventing copying in general with the aid of special protocol conventions. Such protocols have been established, for instance, in the audio application of DAT recorders. As noted above, CD and DAT data formats are substantially identical and, accordingly, multi-generation copying would be possible. In the DAT system, therefore, the CD to be copied is queried for special copy protection information and, if the protection is activated, the DAT recorder is not authorized for copying. Such a method, however, is disadvantageous in that a high degree of discipline with regard to the target devices is necessary. Special anti-copy circuitry must be included in the recorder. Such a system is known as the serial copy management system (SCMS). The end user is not generally interested in those measures. It has been shown that the discipline is not always maintained. In particular, black boxes for filtering the copy-prohibit instruction from the digital signal are widely available. Recently, also, the use of modern PCs makes it possible to easily manipulate such mechanisms and, in the end, to circumvent them.
A prior art copy protection system is described, for instance, in German patent application DE 196 30 755 A1. There, a semiconductor mass storage medium is divided into two memory regions. One of the regions is provided with a non-changeable signature. The signature states whether data can be stored in the primary memory region only with authorization or by anybody. This allows (pirated) copies to be distinguished from the original.
It is accordingly an object of the invention to provide a copy protection method and system, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which safely protects against copying of protected data from one medium onto an equivalent storage medium and the identical use of the copied data as the data on the original storage medium. It is a particular object to prevent the reading-out of information while retaining existing protection mechanisms and the subsequent copying of the deciphered data. Finally, it is a specific object of the novel method to prevent copying from one device onto a device of the same type (e.g. multimedia card), i.e. to render the data on the target device unusable.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of preventing unauthorized copying of data, which comprises:
communicating a unique identification of a device to a content provider;
adding the unique identification as an authenticating signature to a data set to form a signed data set;
copying the signed data set with the unique identification from the content provider to the device;
encoding the data set in the device with the unique identification to form cipher data;
communicating the unique identification of the device to a host; and
reading the cipher data with the host and decoding the cipher data to restore and use the data set in the host.
In accordance with an added feature of the invention, a random number is generated in the host or in the device, and wherein the encoding step comprises encoding the data set with a dynamic key formed with the unique identification and the random number.
In accordance with an additional feature of the invention, the authenticating signature is formed from the unique identification and a private key of the provider, and, following the copying step, the signed data set is checked with the private key against a public key present in the device.
In accordance with another feature of the invention, the signed data set is checked in the device and, if the authenticating signature in the signed data set does not match the unique identification of the device, any output of the data set from the device to the host is blocked.
With the above and other objects in view there is also provided, in accordance with the invention, a copy protection system, comprising:
a device having a unique identification and having an input for receiving signed data formed from a data set and the unique identification;
a controller in the device for authenticating the signed data as authorized data, for storing the data set in the device, and for encoding the data set with a given key to form cipher data;
a host connected to the device, the host receiving the cipher data from the device, deciphering the cipher data, and processing the data set.
In accordance with a concomitant feature of the invention, there is provided a random number generator and a random number generated by the generator is included in the given key to form a dynamic key.
In other words, the invention describes a method in which the device that is to receive data monitors the authorization of the data set to be written by way of a signature, before the data on the device are released for read-out. The signature-check is combined with data enciphering, so that only authenticated data are delivered, in cipher form, from the device to the consuming unit (host).
A part of the signature is a device-specific, non-copyable feature (e.g., the serial number of the device) that identifies each device unambiguously. A further part of the signature is a secret xe2x80x9cprivate keyxe2x80x9d that is only known to the owner of the data set, i.e., the content provider. The xe2x80x9cprivate keyxe2x80x9d is combined with the xe2x80x9cpublic keyxe2x80x9d by way of a one-way function. The public key is present in the device and it cannot be changed.
The device authenticates the data set by way of the signature against its serial number and the public key. The public/private key pair corresponds to a master key that applies to all devices. The device allows writing of only those data that are provided with the valid signature. The signature is established by the owner and the distributor of the data set as follows:
The serial number of the device is communicated to the owner of the data set.
The owner of the data set establishes the signature with the one way function, which contains the following parameters in the argument:
the private key;
the serial number of the target device; and
the data set to be signed.
The user""s device receives the data set and checks the signature. The device then releases the data set for read out only upon the successful checking of the signature. The host is allowed to process only data from the signed part of the device that are encrypted with an agreed-upon algorithm. Non-encrypted data or data that are otherwise encrypted are not usable by the host. Non-authenticated data are not output by the device.
The data set that is stored xe2x80x9cstraightxe2x80x9d in the device is encrypted in dependence on:
the serial number of the device; and
a random number dynamically generated by the host.
Copying of an encoded data set from a device with the protection method to a device in which the (same) protection method is not implemented is possible. However, the data set is not useable because the encryption is device-dependent.
In summary, the invention is essentially a combination of a signature method with an encryption method, which uses variable keys. This achieves the effect that a data set is written only onto a predetermined device and can only be read (deciphered) from that device by the host. Copying of the encrypted data set is thus useless, because the data set is encrypted with the serial number of the device. The result is an effective copy protection system which is far superior to the methods described in the introduction.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a copy protection system and method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.